sub crc16
{
    my($crc) = @_;
    my $length = length($crc);
    $crc = pack("H$length", $crc);
    $ctx = Digest::CRC->new(type => "crc16");
    $ctx->add($crc);
    $ctx = Digest::CRC->new(width => 16, init => 0xFFFF,
           xorout => 0x0000, poly => 0x8005, refin => 1, refout => 1);
    $ctx->add($crc);
    my @crc = split //,$ctx->hexdigest;
    my $crc = join "",@crc[2,3,0,1];
    return $crc;
}